Acupuncture therapy involves the needling of specific points on the body known as acupuncture points. Proper needling elicits a characteristic response known as "de qi". Achieving de qi is considered essential to the therapeutic effect of acupuncture. De qi has a sensory component ("needling sensation")and a simultaneously occurring mechanical component ("needle grasp"). Needle grasp is characterized by a mechanical gripping of the needle by the surrounding tissue. Our long term goal is to determine what tissue components are responsible for needle grasp, and by what mechanisms they operate. Our fundamental hypothesis is that these mechanisms are the same as, or closely related to, those which give rise to acupuncture's therapeutic effect. Future investigations of potential mechanisms will utilize immunohistochemistry, in-situ hybridization, and 3-D reconstruction of biopsies taken before and after induction of needle grasp. Prior to attempting this, however, two more basic questions must be answered: 1)is needle grasp specific to acupuncture points, or can it be elicited equally well at all points on the body? and 2)which tissue is primarily responsible for needle grasp (connective tissue vs. skeletal muscle)? Providing a conclusive answer to these questions is the primary objective of the current work. If acupuncture points have unique physiological characteristics and can be identified by quantifying their needle grasp, this will have important implications on how future studies are carried out. We propose to quantify needle grasp by measuring the peak force required to pull out acupuncture needles ("pull out force") inserted at acupuncture points and control points in 80 normal human volunteers. Needling operations will be carried out by a computer controlled device, eliminating potential investigator bias. All needling parameters (needle insertion speed, insertion depth, etc.) will be consistent with clinical practice. We will also study varying dwell times after insertion and different types of needle manipulation. We will correlate pull out force with depth of needle insertion into muscle and subcutaneous tissue. This will allow us to determine which tissue is most responsible for needle grasp. Our ultimate goal is to determine the relationship between the local tissue response to needling and the therapeutic effect of acupuncture. This will contribute to the fundamental understanding of acupuncture therapy and may lead to improvements in treatments.